examples/src/main/java/org/apache/spark/examples/ml/JavaIndexToStringExample.java
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.spark.examples.ml;

import org.apache.spark.sql.Dataset;
import org.apache.spark.sql.SparkSession;

// $example on$
import java.util.Arrays;
import java.util.List;

import org.apache.spark.ml.attribute.Attribute;
import org.apache.spark.ml.feature.IndexToString;
import org.apache.spark.ml.feature.StringIndexer;
import org.apache.spark.ml.feature.StringIndexerModel;
import org.apache.spark.sql.Row;
import org.apache.spark.sql.RowFactory;
import org.apache.spark.sql.types.DataTypes;
import org.apache.spark.sql.types.Metadata;
import org.apache.spark.sql.types.StructField;
import org.apache.spark.sql.types.StructType;
// $example off$

public class JavaIndexToStringExample {
  public static void main(String[] args) {
    SparkSession spark = SparkSession
      .builder()
      .appName("JavaIndexToStringExample")
      .getOrCreate();

    // $example on$
    List<Row> data = Arrays.asList(
      RowFactory.create(0, "a"),
      RowFactory.create(1, "b"),
      RowFactory.create(2, "c"),
      RowFactory.create(3, "a"),
      RowFactory.create(4, "a"),
      RowFactory.create(5, "c")
    );
    StructType schema = new StructType(new StructField[]{
      new StructField("id", DataTypes.IntegerType, false, Metadata.empty()),
      new StructField("category", DataTypes.StringType, false, Metadata.empty())
    });
    Dataset<Row> df = spark.createDataFrame(data, schema);

    StringIndexerModel indexer = new StringIndexer()
      .setInputCol("category")
      .setOutputCol("categoryIndex")
      .fit(df);
    Dataset<Row> indexed = indexer.transform(df);

    System.out.println("Transformed string column '" + indexer.getInputCol() + "' " +
        "to indexed column '" + indexer.getOutputCol() + "'");
    indexed.show();

    StructField inputColSchema = indexed.schema().apply(indexer.getOutputCol());
    System.out.println("StringIndexer will store labels in output column metadata: " +
        Attribute.fromStructField(inputColSchema).toString() + "\n");

    IndexToString converter = new IndexToString()
      .setInputCol("categoryIndex")
      .setOutputCol("originalCategory");
    Dataset<Row> converted = converter.transform(indexed);

    System.out.println("Transformed indexed column '" + converter.getInputCol() + "' back to " +
        "original string column '" + converter.getOutputCol() + "' using labels in metadata");
    converted.select("id", "categoryIndex", "originalCategory").show();

    // $example off$
    spark.stop();
  }
}
